My '85 300SD makes a clunk as it downshifts when I approach a stop light. After reading thru posts on similar issues in the forum, I've been going thru my vacuum lines looking for leaks.

I think I've found a leak, but I'm not sure where this vacuum line terminates. It's red/green and is plugged into a 4-way junction near the brake booster. When I unhook this line and plug up the receptacle on the junction, I measure 20 Hg of vacuum at the vacuum supply line to the transmission modulator. When the red/green line is attached, I measure no vacuum at the vacuum supply to the transmission.

Strangely, when I hook up my mighty vac to this mysterious red/green line, it holds vacuum.

I've attached a few images. Please forgive how I've named things in the pictures. I don't know the proper names.

If someone could identify this mysterious red/green line for me, or point me to where it is illustrated on some diagram (I looked and couldn't find it), I would really appreciate it.

Thanks,

Zac

P.S. This post seems similar, but I'm not sure if we're describing exactly the same thing.
http://www.peachparts.com/shopforum/showthread.php?t=237683

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